JPH04233370A - Image forming device - Google Patents

Abstract

PURPOSE:To maintain the correct image obtained in the beginning continuously even after time elapses by setting separately light beam power in a period for executing the image formation, and allowing it to correspond to deterioration of a photosensitive body. CONSTITUTION:Digital DATA corresponds to a digital value which is set so that a light beam which becomes the optimal light quantity at the time of detection of BD is obtained from a semiconductor laser 15. In such a state, the light quantity of the light beam photodetected by a photodetecting part 17 is monitored by a control part 10, and at the time of detection of BD an optimal digital signal DATA1 is set to an FF 2211 of a laser beam driver 12. In this case, by using the light beam, a light output at the time of detecting the timing of image formation and a light output in an image forming area are set separately. When light beam power for executing this image formation is set in accordance with deteoration of a photosensitive body, the light potential is adjusted, and a correct image obtained in the beginning is obtained even after time elapses.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus that forms an image using a light beam.

0002

[Prior Art] Conventionally, in an image forming apparatus using a laser element, the optical output of the laser for generating the image forming timing (horizontal synchronizing signal or BD) and the optical output of the laser for forming the image are the same. there were.

0003

[Problems to be Solved by the Invention] FIG. 8 shows a graph of changes in the photoreceptor over time. The horizontal axis shows the number of copies, and the vertical axis shows the potential of the photoreceptor. 801 indicates dark potential. 802 (corresponding to white on the transfer paper) indicates a write potential. That is, it indicates the potential of the photoreceptor when the laser emits light. Figure 8
As can be seen from , the change in light potential over time is much larger than the change in dark potential. This dark potential fluctuation has a large effect on the density of the transferred image, causing a problem that it becomes impossible to obtain a proper image. That is, as the write potential decreases, the black density increases, causing a problem in which the initial intermediate level is destroyed (shifted toward black). Therefore, the optical output of the laser is lowered to increase the light potential, and adjustments are made to increase the light potential so that the proper image obtained initially can be obtained even after a period of time has elapsed.

However, when the optical power is narrowed down by adjusting the optical output of the laser, it becomes impossible to detect the timing of image formation, resulting in the inconvenience that the apparatus becomes inoperable.

[0005]

[Means and effects for solving the problems] According to the present invention, a means is provided for individually setting the light output when detecting the timing of image formation using a light beam and the light output in the image forming area. It is something.

[0006]

Embodiment FIG. 1 is a main control block diagram illustrating the control configuration of an image forming apparatus to which an embodiment of the present invention is applied, in which 1 is a light scanning optical system (optical scanning system); , an imaging lens 3, a semi-moving laser 15, and a collimator lens 14. The polygon mirror 2, which rotates at a constant speed, deflects the laser beam into a parallel beam in the direction of the arrow through the collimator lens 14, forming an image. A photosensitive member (photosensitive drum) 4 is scanned in the direction of an arrow S through a lens 3. Reference numeral 5 denotes a laser beam, which corresponds to a laser beam scanning an area other than the desired scanning width, and in this embodiment, a light amount detection process, which will be described later, is performed on a laser beam 6 scanning within the scanning width. A beam detector 9 (constituting a detection means) receives the laser beam 5 deflected and scanned by the polygon mirror 2, and outputs a beam detection signal serving as an image writing timing signal in the main scanning direction. Note that 12 is a laser beam driver, and 16 is a BD signal generation circuit.

FIG. 2 is a circuit block diagram illustrating the detailed configuration of the laser beam driver 12 shown in FIG. 1, and the same components as in FIG. 1 are given the same reference numerals. Setting control of the drive current applied to the semiconductor laser 15 will be explained below. A modulation signal 2208 based on video data and a blanking signal 2209 are sent, input to an OR circuit 2207, and input via a buffer 2201 to one transistor 2202 constituting an operating circuit. The other transistor 2203 turns the semiconductor laser 15 ON/OFF. R1 to R7 and R9 are resistors.

On the other hand, transistor 2204 supplies constant current to both transistors 2202 and 2203.

The operational amplifier 2205 includes a constant voltage source 220
The voltage applied to resistor R5 for monitoring the current of transistor 2204 is supplied to the inverting terminal (- side terminal), and the voltage to flow a predetermined current is supplied to transistor 2204. do. On the other hand, 221
0 is a D/A converter, flip-flop (F/F) 22
11 is converted into an analog DC current, and the converted analog DC current is input to the non-inverting terminal of the operational amplifier 2205. flipflop 22
11 is a digital signal DA output from the control unit 10
Holds TA1 and DATA2. Note that the digital signal D
ATA1 corresponds to a digital value that is set so that a light beam with an optimum light intensity is obtained from the semiconductor laser 15 during BD detection. That is, the control section 10 monitors the amount of light beam received by the light receiving section 17 (usually configured integrally with the laser element 15 and includes a light receiving element that receives the back beam of the laser element 15), and when detecting a BD,
Flip-flop 2211 of laser beam driver 12
The optimum digital signal DATA1 is set. This control section 10 includes a counter 10a and registers 10b, 10.
c, and operates as described below.

Furthermore, the control section 10 sets a digital signal DATA2 to the flip-flop 2211 when scanning the image forming area after detecting the BD. The digital signal DATA2 corresponds to a digital value that is set so that a light beam with an optimum light amount is obtained from the semiconductor laser 15 during image formation. A constant voltage source 2206 supplies the reference potential divided by resistors R6 and R7 to the non-inverting input of the operational amplifier 2205.

FIG. 3 is a circuit block diagram illustrating the detailed configuration of the light receiving section 16 shown in FIG. 2, and the same components as in FIG. 2 are given the same reference numerals.

The configuration and operation will be explained below.

[0013] The laser light incident on the photodetector has a current of -
It is converted into an electrical signal by a voltage conversion circuit (I/V conversion circuit) 2225 and input to a sample hold circuit (S/H) 2227. The signal input to the sample and hold circuit 2227 is sampled and held by a timing signal from a synchronous control circuit (not shown), and then sent to the buffer circuit 2228.
is input to the control unit 10 via A/D conversion.
The data is read by a CPU (not shown) in the control unit 10. Note that 2229 is an output signal.

In FIG. 4, BD is a beam detect signal, VCLK is a video clock, and VIDEO is a video signal.

Next, the image forming processing operation in the image forming apparatus according to the present invention will be explained with reference to FIG.

FIG. 5 is a flowchart illustrating an example of an image forming process procedure in an image forming apparatus according to the present invention. Note that (1) to (9) indicate each step. Before starting the image forming operation, first step (1) is performed.
) a pre-rotation takes place. In this embodiment, since image formation is performed by electrophotography, the pre-rotation is performed in order to uniformly charge the photoreceptor 4. In parallel with this pre-rotation, it is determined in step (2) whether or not the count value of the counter 10a has reached a predetermined number of rotations. This counter 1
0a counts the number of image formations of this device,
For example, it is configured to count vertical synchronization signals.

[0017] The count 10a is, for example, 100 times, 200
Once a predetermined value such as 300 times, 500 times, 1000 times, 1500 times, etc. is counted, the process moves to step (3). Note that if the counter 10a has not counted the predetermined value, the process moves to step (4), which will be described later.

In step (3), a value corresponding to the count value of the counter 10a is set in the register 10c. Photoreceptor 4
Since there is a relationship between the change over time and the number of image formations as shown in FIG. 8 described above, the amount of beam light must be set according to this count value. In the photoreceptor of this embodiment, the amount of beam light decreases as the number of image formation increases. Therefore, the target light quantity value set in the register 10c also becomes smaller as the number of image formations increases.

Next, in step (4), APC (automatic light amount control) is performed based on the register 10c. That is, the light amount control is performed so that the actual light amount becomes equal to the target light amount value in the register 10c. Specifically, DATA2
DAT when the detected value of light emission amount based on DATA2 matches the target light amount value by gradually increasing the value of
A2 is held in the control circuit 10 (step (5)).

In step (6), APC is performed in the same way as the APC described above based on the register 10b. As a result of the APC, DATA1 is held in the control circuit 10 (step (7)).

[0021] When the forward rotation is completed (step (8)
)) and performs an image forming operation (step (9)). During the image forming operation, forced laser light emission is performed while scanning the non-image forming area for BD detection, but the light emission at this time is performed with a drive current based on DATA1, and ON light emission while scanning the image forming area is based on DATA2. This is done with a drive current based on .

In this embodiment, the value in the register 10b is not changed depending on the number of image formations, so even if the number of image formations increases, the BD will not become undetectable. Furthermore, deterioration in image quality due to deterioration of the photoreceptor due to an increase in the number of image formations can be prevented.

[0023] The above-mentioned operation is performed in the case of pre-rotation, but it is also performed during so-called paper spacing. Further, the APC operation (at least one of steps (4) and (6)) may be performed during scanning of a non-image forming area, or may be performed during pre-rotation or scanning of a non-image forming area between sheets. good.

(Other Embodiments) In the above embodiments, B
Although we have described the case where the CPU of the control unit 10 switches the driving power of the laser at the time of D detection and the time of image formation as necessary, as shown in FIG.
/F) 2213 is set with digital data corresponding to the driving power during image formation, and the flip-flop (F/F) 2213 is set with digital data corresponding to the driving power during image formation.
) 2214 to set digital data corresponding to the laser power at the time of BD detection, and selector 221
Blanking is performed by selecting input terminals A and B of the selector 2212 based on the blanking signal 2209 input to the OR circuit 2207. Signal 2209 is in the valid state (Blanking signal 2 shown in FIG.
209 is in the ON state), it becomes possible to output digital data corresponding to the laser power at the time of BD detection to the D/A converter 2210.

Furthermore, in the above embodiment, the output signal 2229 from the BD signal generation circuit 16 is once sent to the control section 10 via the A/D converter.
The case has been described in which the digital data is captured while being converted and the CPU etc. executes the light amount control according to this digital data.As shown in FIG. 7, an analog switch 2215 is provided in the laser beam driver 12 shown in FIG. By combining the BD signal generation circuit 16 shown in FIG. 1 with the configuration, it becomes possible to control the amount of light at high speed while reducing the control burden on the CPU.

That is, the laser light incident on the light receiving element 19 is converted into an electric signal by the current-voltage conversion circuit 2225 and input to the comparator 2226 and the amplifier 2216. The comparator 2226 compares the signal with a reference voltage and shapes the waveform to obtain a reference signal HSYNC in the main scanning direction of the laser. Further, the amplifier 2216 amplifies the signal differentially from the reference voltage, samples and holds the sample and hold circuit 2227, and inputs the signal to the input terminal B of the analog switch 2215.

FIG. 9 shows yet another embodiment of the invention, in which the same reference numerals are used for the same parts as in FIG. In this embodiment, a potential detector 18 for measuring the surface potential of the photosensitive drum is provided in place of the counter 10a.

In this embodiment, for example, when the power is turned on, the image shown in FIG.
Detect the dark potential and light potential as shown in
Based on this, the value to be set in register 10c is updated. The other operations are the same as in Figure 2, so
The explanation will be omitted here. In this case, a display may be displayed to instruct conversion of the photoreceptor when the deterioration of the photoreceptor exceeds a predetermined level.

[0029]

Effects of the Invention As explained above, by using a light beam to change the light output when detecting the start timing (BD) of image formation and the light output in the image forming area, changes in the photoreceptor over time can be reduced. This has the effect of eliminating the situation where image forming timing (BD) cannot be detected due to power adjustment of the light beam that occurs when correcting sensitivity deterioration caused by.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an image forming apparatus to which an embodiment of the present invention is applied.

2 is a circuit block diagram of the laser beam driver 12 shown in FIG. 1. FIG.

3 is a circuit block diagram of a detailed configuration of the light receiving section 16 shown in FIG. 2. FIG.

FIG. 4 is an operation timing chart of this image forming apparatus.

FIG. 5 is a flowchart for explaining the operation of the control unit 10.

FIG. 6 is a circuit block diagram showing the main part configuration of another embodiment of the present invention.

FIG. 7 is a circuit block diagram showing the main configuration of still another embodiment of the present invention.

FIG. 8 is a graph for explaining problems in the prior art.

FIG. 9 is a circuit block diagram showing the main configuration of still another embodiment of the present invention.

[Explanation of symbols]

4 Photosensitive drum 9 Beam detector 10 Control section 10a Counter 10b, 10c register 18 Potential detector

Claims (3)

[Claims] 1. A light source that emits a light beam, a deflection means that deflects the light beam emitted from the light source, and an image forming means that irradiates a photoreceptor with the deflected light beam to form an image. In the image forming apparatus, a detection means for detecting the light beam changed by the deflection means at a predetermined position; a light beam power in a first period including a timing at which the light beam is detected by the detection means; Different from the first period, the light beam power for the second period for performing image formation is individually set; An image forming apparatus characterized in that settings are made according to. 2. The image forming apparatus according to claim 1, further comprising a counting means for counting the number of image forming operations,
The image forming apparatus is characterized in that the setting means sets the light beam power for the second period according to the count value of the counting means. 3. The image forming apparatus according to claim 1, further comprising potential detection means for detecting the potential of the photoreceptor, and the setting means is configured to:
An image forming apparatus characterized in that the light beam power for the second period is set.